The present invention generally relates to the field of semiconductor packaging, and more particularly to apparatus for attaching chip mounted heat sinks to chip packages such as ball grid array (BGA) type chip packages or the like, wherein the apparatus provides an electromagnetic channel (EMC) ground interconnect with the chip""s integrated circuit die so that the heat sink does not become an efficient electromagnetic interference (EMI) radiator.
Current semiconductor packaging technology involves mounting integrated circuit chips on chip carriers such as ceramic substrates or assembling the chips into plastic packages which provide the necessary pin or lead input/output connections. Wire bonding and flip chip bonding provide two principal methods of connecting chips to such substrates or packages. Wire bonding utilizes short wires (wire bonds), typically formed of aluminum or gold, which are connected by ultrasonic bonding from wire bond pads (input/output (I/O) pads) on the chip to metal pads on a chip carrier or, for plastic packages, to leads of a lead frame. Flip chip bonding utilizes solder balls placed on the chip die. The chip die is then xe2x80x9cflippedxe2x80x9d over onto the chip carrier and the solder melted.
Ball Grid Array (BGA) packages connect to the Printed Circuit Board (PCB) through an array of solder balls beneath the packages. This area array of solder balls reduces package size and increases lead pitch, leading to higher assembly yields. Because of the increasing density of the integrated circuit dies utilizing BGA packaging, it is often desirable to mount a heat sink directly to the BGA package, in order to dissipate heat generated by the die. However, by attaching such heat sinks to the die within the package, an electromagnetic interference (EMI) radiator or antenna may be created, which may adversely affect function of the integrated circuit die or other components mounted to the printed circuit board. Presently, EMI radiation through the heat sink is reduced by soldering wires from the heat sink to ground points on the printed circuit board in order to ground the heat sink to the circuit board. Thus, there currently exists no way to efficiently automate the placement of the heat sink, which requires a metal conductor from the heat sink to the printed circuit board.
Consequently, it is desirable to provide an apparatus for attaching chip mounted heat sinks to chip packages, wherein the apparatus provides an EMC ground interconnect with the chip""s integrated circuit die so that the heat sink does not become an efficient EMI radiator. It is further desirable, that this apparatus facilitate efficient automation of attachment of the heat sink to the chip package, and eliminate the requirement of a metal conductor from the heat sink to the printed circuit board.
Accordingly, the present invention is directed to apparatus for attaching chip mounted heat sinks to chip packages such as ball grid array (BGA) type chip packages, or the like, wherein the apparatus provides an EMC ground interconnect with the chip""s integrated circuit die so that the heat sink does not become an efficient EMI radiator. In an exemplary embodiment, ground bumps are formed on the die substrate of the chip package and on the heat mating surface of the heat sink to be attached to the package. The ground bumps formed on the die protrude into the body of dimples formed in the encapsulation cap of the chip package to make thermal/electrical ground contact with the ground bumps formed on the heat mating surface of the heat sink for electrically grounding the heat sink to the die. In this manner, an EMC ground interconnect between the heat sink and the integrated circuit die is created.
It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.